The spread of W-CDMA (Wideband Code Division Multiple System) type mobile communication systems is so obvious that the population coverage of W-CDMA type mobile communication system is nearly 100%. On the other hand, the coverage of W-CDMA type mobile communication system for indoor use is as yet not high. This is because radio waves do not easily enter from outdoors to indoors, and cost is high to install and operate a base station for indoor use.
In this environment, a base station (BTS: Base Transceiver Station), called a “femto cell”, which is smaller than a conventional base station, has recently been made available. It is assumed that this micro-miniature base station (hereafter called micro-miniature BTS device) will be used in a home or office, and supports W-CDMA, enables simultaneous communication for about 4 users, and is inexpensive.
By installing this micro-miniature BTS device in skyscrapers and in underground facilities which conventional base stations cannot fully cover, indoor coverage can be improved without increasing operation cost.
However, for a general mobile communication system depicted as a related art in FIG. 1, to control base stations, it is necessary to accommodate base stations BTS #1, #2, . . . #n by a base station control device (RNC: Radio Network Controller, hereafter called “RNC device”) 1, which is connected to the core network CN. However the number of base stations BTS #1, #2, . . . #n which one RNC device 1 can control is limited, and this number is roughly several hundred.
First of all, a publically known technology is an invention disclosed in Japanese Laid-open Patent Publication No. 4-337997.
The invention disclosed in Japanese Laid-open Patent Publication No. 4-337997 is a communication system using femto cells. For the connection of femto cells, however, only connections between an RNC device and base stations are referred to.
Another publically known technology is an invention disclosed in Japanese Laid-open Patent Publication No. 2004-179981. According to this invention, neighborhood mobile terminals form a group, where a plurality of mobile terminals transmit and receive voice and packets as if they are one pseudo-terminal. However, this technology makes mobile terminals “appear” as one terminal at the network side, and in the disclosure of this invention nothing is mentioned on how to manage base stations.
Therefore, a new accommodating method is necessary to accommodate many (e.g. several thousand) micro-miniature BTS devices.